150 THE CEARA RUBBER TREE 



diluted latex is rendered just acid by the addition of 

 acetic acid, but this is not necessary unless ammonia has 

 been used in collecting it. This method is very con- 

 venient for the preparation of the rubber in biscuit form. 

 In order to obtain the best results the latex should be 

 weU diluted with water and the rubber obtained should 

 be thoroughly washed. 



Yield of Rubber. — Considerable variation has been 

 observed in the yield of rubber furnished by cultivated 

 Ceara trees of the same age growing in the same locality, 

 and m order to obtain a trustworthy estimate for the 

 yield of a plantation it is necessary to take the average 

 of a considerable number of trees. Thus, for example, 

 m East Africa, smgle trees nme to ten years old are stated 

 to have jdelded as much as 10 to 12 lb. of dry rubber in a 

 year, whereas 1 lb. per annum is a high average yield 

 from trees of this age, and the jdeld from plantations of 

 trees three j^ears old and upwards is about 4 oz. of dry 

 rubber per tree annually. In the following account a 

 summary is given of the yields obtamed in different 

 countries : 



Brazil. — The average yield of rubber from cultivated 

 Ceara trees in Brazil has been given as 300 kilograms per 

 hectare, and as the trees are usually planted about 2,500 

 to the hectare, this is equivalent to a little more than 

 4 oz. per tree per annum. 



Ceylon. — The superintendent of an estate upon which 

 a large number of Ceara trees are growing has expressed 

 the opinion that | to | lb. of diy rubber per tree is as 

 much as the trees will yield annually, if they are to be 

 tapped for long periods and retain their vitality. This 

 estate has exported Ceara rubber since 1886. 



East Africa. — In German East Africa there are about 

 60,000 acres of Ceara trees under cultivation, and Professor 

 Zimmermann, of the Biologisch Landwirtschaft lichen 

 Institut at Amani has published the following figm^es as 

 represent mg the average yields of chy rubber from trees 

 of different ages : 



Age of trees. Kilograms of rubber lb. of rubber 



Years. per hectare. per acre. 



4 50 44 



5 100 88 



6 150 132 



